Mu-so Qb Unmasked

‘I reckon I’m on around 250 stored iterations of the signal processing in search of just the right sound, and for every one of those there were probably ten variations I rejected and didn’t bother keeping because I knew we could do better. So that’s thousands of iterations before we hit on the right one.’

That’s Naim Technical Director Roy George talking about the laborious and painstaking development process behind the new Mu-so Qb, and he’s only referring to the digital ‘tuning’ employed to keep the final sound of the new product true to its Naim heritage – despite the fact that the sound is coming from an ultra-compact system designed to fit into spaces where even the original Mu-so can’t go.

Discussing Mu-so Qb with the team behind the project – Roy George, lead engineer Matthieu Guilloux and Group Director of Design Simon Matthews – it’s clear that there were three vital aspects to the development of the new model: it needed to have a smaller footprint than the very successful original Mu-so, be even more affordable, and above all remain true to the Naim sound.

Oh, and it had to appeal to buyers new to Naim, attracting them to the brand, while still offering a solution for those Naim enthusiasts looking for an ‘extra zone’ for existing ND or Uniti-based multiroom network music systems.

Achieving all this with the original Mu-so was hard enough; pulling off the same feat in an even smaller system was going to be really tricky. It required the use of new materials and engineering solutions, an all-new design that went far beyond a simple downscaling, and months of tuning work to ensure a level of performance on par with that of its big brother.

As Roy George says, ‘There was a lot of computer simulation involved, using the LspCAD tool for the design of speaker boxes, and a lot of negotiation between me on the engineering side and Simon on the design side, trying to get the performance out of what is a fairly small box. We found that even a few millimetres change in size could make a major change to way the product would sound.’

Or as Matthews puts it, the end result is, ‘As small as I wanted it, and as small as Roy was happy with to deliver a true Naim sound.’

At the outset, it was clear that, while some of the solutions developed for Mu-so could be carried over to the Qb, the smaller cubic shape required just as much original thinking. As Simon Matthews explains, ‘Early on it was clear that the conventional handmade wooden enclosure of Mu-so wasn’t going to work here, given the complex speaker layout we were considering.’

The new design wouldn't support the ported bass-tuning of Mu-so, not least due to the smaller footprint of the system, clarified Roy George, ‘and above all we wanted to develop a sound with an “out of the box” ability to fill a room, despite the drive units being much closer together.’

Simon Matthews added that, ‘You can’t put a port in a box this size and tune it successfully: it either has to be tiny, in which case it stops behaving as a port, it chokes, or it just becomes too big to fit.’

The result is at least two elements that are completely new to both Mu-so and Naim: the main ‘skeleton’ of Qb is an extremely complex single piece of glass-loaded polycarbonate/ABS, the ‘open box’ shape the result of extensive computer modelling, and fabricated using a complex injection moulding tool; the bass meanwhile is tuned not with a port but using a pair of ‘side-firing’ auxiliary bass radiators, or ABRs – just like extra bass speakers, but passive and driven by the movement of the main woofer.

Strong and rigid though the material chosen for that main chassis may be, incorporating seven drivers into its compact dimensions necessitated a lot of ‘holes’, with relatively little supporting structure around them. The solution, while logical, was less than simple: every element of Qb plays a structural role. And that goes from the clear acrylic platform on which it’s built to the recess on the top in which the main multifunctional control (carried over from both Mu-so and the flagship Statement amplifier) sits, and from the rear heatsink onto which the main electronics are mounted through to the drive units themselves.

The ABRs, for example, are usually fairly simple units and of lightweight construction, composted of little more than compliantly-mounted panels able to radiate along with the music. Here they use a flat aluminium diaphragm and are built on a substantial chassis complete with a rigid ‘basket’ to the rear, featuring ‘spider’ suspension that works with the surround linking panel to chassis, to keep the movement of the ABR under control, ensuring a more accurate pistonic motion.

This enables the ABR, just like the front-mounted main bass driver – which is also an oval unit – to add rigidity to the main structure, more than compensating for any lack of stiffness created by the apertures in which the units are mounted. The woofer is also mounted to the floor of the main enclosure moulding, again adding structural integrity and ensuring it’s protected even if the Qb is put down rather enthusiastically!

The midrange drivers, which use performance-enhancing design elements such as the copper-capped poles for the magnet system, are similarly designed with stiffness and rigidity in their chassis: moulded housings behind (or buckets, as the team describes them) to isolate them from the bass driver and also strengthen the front panel.

Meanwhile, the two high-frequency drivers are mounted into the complex front baffle shape to spread sound more effectively into the room – aided, of course, by all that clever DSP stuff. The DSP runs on a powerful processor capable of 150MIPS – that means up to 150 million instructions can be handled every second, monitoring every aspect of the drivers’ performance, from equalisation to time delays and so on.

As Roy explains it, ‘I've now authored the DSP for Mu-so and the systems for probably 20 Bentley cars, so that history was very beneficial here.’ That, along with experience gained in the use of drive units in small enclosures (such as car doors), and Class D amplification, is an example of how what may seem like individual aspects of the Naim business – as diverse as wireless music systems and the Naim for Bentley project, soon to hit the road as a major feature of the new Bentayga SUV – can inform and assist each other.

And how does he work? Well, his comments at the beginning should give you some idea of how long he’s been obsessing with Qb’s sound: it runs into many hundreds of hours, ‘and when we hit on a DSP configuration that shows promise, then we go on to listening with a number of genres of music, so that can take quite a long time.’

When we speak, there’s still a day or so until the sound needs final sign-off, ...‘so that means I’ll still be working on it for the next day and a half, right up until the last minute. You never know, that final two hours – you might find something quite important…’

It’s one of the beauties of DSP, that work can carry on like this in tandem with the assembly of pre-production trial samples of the product: when the finished tune is agreed, it can then be uploaded into the product in a similar way that Naim’s ND- and Uniti products can have their DSP audio tuning adjusted as part of firmware upgrade – ‘only rather faster’, says George.

A major part of the tuning of the Qb is to ensure a consistent ‘voice’ with the original Mu-so; it’s important if you’re using the Qb as a second zone system that the tonality of the sound shouldn’t change when you move from zone to zone.

Each drive unit is powered by its own channel of amplification, as in the original Mu-so, with the main difference being that Qb has five, not six, channels, delivering 50W apiece to the midrange and high-frequency drivers, and 100W to the bass, instead of the 6 x 75W of the ‘big’ Mu-so.

Matthieu Guilloux explains that this lower output allowed the power supply requirements for Qb to be reduced, helped by the fact that the custom-designed drive units have lower impedance and so are less power-hungry, and that the extra power for the woofer was achieved simply by using both sides of the amplifier chip for a single woofer, rather than driving two as in Mu-so.

The amplifiers here are the same as those used in the larger model: originally chosen by listening tests, they have proved to be reliable in service, and with the intention of Qb sounding as similar possible, the team saw no reason to change.

Lower power requirements also mean less heat, which is good for reliability and stability, as well as simplifying the job of the heatsink, to which the output transistors are directly coupled. Matthieu explains that factory testing over on/off cycles and ambient temperatures ranging from -20C to 80C has been going on for many weeks, chilling the chamber as the unit is turned off and is itself cooling, then ramping the temperature back up with the Qb playing pink noise at full volume.

This accelerated life-testing means that before the Qb hits the shops, it will have proven itself over more than five years of operation – even if when running at full tilt with the chamber near 80C, meaning the temperature inside the Qb was well into three figures, there's been some experience of the glues used inside the new product becoming a little soft! Fortunately those conditions aren't going to be replicated in the real word.

The final part of the assembly is extensive gasketing between the basic five-sided chassis ‘box’, the top-panel and the heatsink/rear panel, each of which is assembled separately and then installed as a complete unit, to ensure the whole product is airtight. Rigidity is ensured by a complex series of mechanical connections between these sections and the main chassis, completed with multiple bolts to hold the whole thing together, where lesser products might just use a snap-fit assembly.

Completing the structural stuff is that clear acrylic base, carrying the Naim logo and providing the impression that the Qb is floating: it is bonded in place, further stiffening the entire ‘cabinet’.

The heatsink rear panel contains precisely routed antennae for wireless connectivity and the physical sockets – functionality is identical to that on the original Mu-so, with UPnP, AirPlay for Apple Music, integrated streaming services (Spotify and Tidal) and Internet radio via wired Ethernet or Wi-Fi, plus aptX-capable Bluetooth, along with optical digital, analogue and iOS-compliant USB sockets.

And of course being a Mu-so, the Qb has a removable grille, allowing the owner to customise the product in one of four colours – (black as standard), with Deep Blue, Vibrant Red and Burnt Orange optional – or just leave it uncovered to show off all the clever stuff going on within.

The grille here is rather more complex than that on the original Mu-so, consisting of a three-sided hinged wrap, still adorned with the same ‘wave’ motif seen on the first Mu-so. This process involved some pretty serious design and engineering in itself, combining as it does ABS panels with polypropylene hinges over-moulded, with the grille-cloth itself tensioned and welded in place.

As became clear when talking to the team, Mu-so Qb may be the company’s most affordable system, designed to introduce even more people to the brand, but this is very much a Naim product through and through, designed, developed and engineered in as painstaking a fashion as every other Naim system.

It’s simple, compact and attractive, but at the same time has 40+ years of Naim expertise behind it, and is every bit as capable of making a statement as – well, Naim’s Statement.

Mu-so Qb is now available at your local retailer.